Add independent spinbox arrow step precision

Backported from the `master` branch, with a property hint added.

doc/classes/SpinBox.xml

@@ -39,6 +39,9 @@
 		<member name="align" type="int" setter="set_align" getter="get_align" enum="LineEdit.Align" default="0">
 			Sets the text alignment of the [SpinBox].
 		</member>
+		<member name="custom_arrow_step" type="float" setter="set_custom_arrow_step" getter="get_custom_arrow_step" default="0.0">
+			If not [code]0[/code], [code]value[/code] will always be rounded to a multiple of [code]custom_arrow_step[/code] when interacting with the arrow buttons of the [SpinBox].
+		</member>
 		<member name="editable" type="bool" setter="set_editable" getter="is_editable" default="true">
 			If [code]true[/code], the [SpinBox] will be editable. Otherwise, it will be read only.
 		</member>

scene/gui/spin_box.cpp

@@ -79,7 +79,8 @@ void SpinBox::_line_edit_input(const Ref<InputEvent> &p_event) {
 void SpinBox::_range_click_timeout() {
 	if (!drag.enabled && Input::get_singleton()->is_mouse_button_pressed(BUTTON_LEFT)) {
 		bool up = get_local_mouse_position().y < (get_size().height / 2);
-		set_value(get_value() + (up ? get_step() : -get_step()));
+		double step = get_custom_arrow_step() != 0.0 ? get_custom_arrow_step() : get_step();
+		set_value(get_value() + (up ? step : -step));
 
 		if (range_click_timer->is_one_shot()) {
 			range_click_timer->set_wait_time(0.075);
@@ -109,6 +110,8 @@ void SpinBox::_gui_input(const Ref<InputEvent> &p_event) {
 
 	Ref<InputEventMouseButton> mb = p_event;
 
+	double step = get_custom_arrow_step() != 0.0 ? get_custom_arrow_step() : get_step();
+
 	if (mb.is_valid() && mb->is_pressed()) {
 		bool up = mb->get_position().y < (get_size().height / 2);
 
@@ -116,7 +119,7 @@ void SpinBox::_gui_input(const Ref<InputEvent> &p_event) {
 			case BUTTON_LEFT: {
 				line_edit->grab_focus();
 
-				set_value(get_value() + (up ? get_step() : -get_step()));
+				set_value(get_value() + (up ? step : -step));
 
 				range_click_timer->set_wait_time(0.6);
 				range_click_timer->set_one_shot(true);
@@ -131,13 +134,13 @@ void SpinBox::_gui_input(const Ref<InputEvent> &p_event) {
 			} break;
 			case BUTTON_WHEEL_UP: {
 				if (line_edit->has_focus()) {
-					set_value(get_value() + get_step() * mb->get_factor());
+					set_value(get_value() + step * mb->get_factor());
 					accept_event();
 				}
 			} break;
 			case BUTTON_WHEEL_DOWN: {
 				if (line_edit->has_focus()) {
-					set_value(get_value() - get_step() * mb->get_factor());
+					set_value(get_value() - step * mb->get_factor());
 					accept_event();
 				}
 			} break;
@@ -156,8 +159,8 @@ void SpinBox::_gui_input(const Ref<InputEvent> &p_event) {
 	if (mm.is_valid() && mm->get_button_mask() & BUTTON_MASK_LEFT) {
 		if (drag.enabled) {
 			drag.diff_y += mm->get_relative().y;
-			float diff_y = -0.01 * Math::pow(ABS(drag.diff_y), 1.8f) * SGN(drag.diff_y);
+			double diff_y = -0.01 * Math::pow(ABS(drag.diff_y), 1.8f) * SGN(drag.diff_y);
-			set_value(CLAMP(drag.base_val + get_step() * diff_y, get_min(), get_max()));
+			set_value(CLAMP(drag.base_val + step * diff_y, get_min(), get_max()));
 		} else if (drag.allowed && drag.capture_pos.distance_to(mm->get_position()) > 2) {
 			Input::get_singleton()->set_mouse_mode(Input::MOUSE_MODE_CAPTURED);
 			drag.enabled = true;
@@ -252,6 +255,14 @@ void SpinBox::apply() {
 	_text_entered(line_edit->get_text());
 }
 
+void SpinBox::set_custom_arrow_step(double p_custom_arrow_step) {
+	custom_arrow_step = p_custom_arrow_step;
+}
+
+double SpinBox::get_custom_arrow_step() const {
+	return custom_arrow_step;
+}
+
 void SpinBox::_bind_methods() {
 	//ClassDB::bind_method(D_METHOD("_value_changed"),&SpinBox::_value_changed);
 	ClassDB::bind_method(D_METHOD("_gui_input"), &SpinBox::_gui_input);
@@ -262,8 +273,10 @@ void SpinBox::_bind_methods() {
 	ClassDB::bind_method(D_METHOD("get_suffix"), &SpinBox::get_suffix);
 	ClassDB::bind_method(D_METHOD("set_prefix", "prefix"), &SpinBox::set_prefix);
 	ClassDB::bind_method(D_METHOD("get_prefix"), &SpinBox::get_prefix);
-	ClassDB::bind_method(D_METHOD("set_editable", "editable"), &SpinBox::set_editable);
+	ClassDB::bind_method(D_METHOD("set_editable", "enabled"), &SpinBox::set_editable);
 	ClassDB::bind_method(D_METHOD("is_editable"), &SpinBox::is_editable);
+	ClassDB::bind_method(D_METHOD("set_custom_arrow_step", "arrow_step"), &SpinBox::set_custom_arrow_step);
+	ClassDB::bind_method(D_METHOD("get_custom_arrow_step"), &SpinBox::get_custom_arrow_step);
 	ClassDB::bind_method(D_METHOD("apply"), &SpinBox::apply);
 	ClassDB::bind_method(D_METHOD("_line_edit_focus_enter"), &SpinBox::_line_edit_focus_enter);
 	ClassDB::bind_method(D_METHOD("_line_edit_focus_exit"), &SpinBox::_line_edit_focus_exit);
@@ -275,6 +288,7 @@ void SpinBox::_bind_methods() {
 	ADD_PROPERTY(PropertyInfo(Variant::BOOL, "editable"), "set_editable", "is_editable");
 	ADD_PROPERTY(PropertyInfo(Variant::STRING, "prefix"), "set_prefix", "get_prefix");
 	ADD_PROPERTY(PropertyInfo(Variant::STRING, "suffix"), "set_suffix", "get_suffix");
+	ADD_PROPERTY(PropertyInfo(Variant::REAL, "custom_arrow_step", PROPERTY_HINT_RANGE, "0,10000,0.0001,or_greater"), "set_custom_arrow_step", "get_custom_arrow_step");
 }
 
 SpinBox::SpinBox() {

scene/gui/spin_box.h

@@ -49,6 +49,7 @@ class SpinBox : public Range {
 	virtual void _value_changed(double);
 	String prefix;
 	String suffix;
+	double custom_arrow_step = 0.0;
 
 	void _line_edit_input(const Ref<InputEvent> &p_event);
 
@@ -90,6 +91,8 @@ public:
 	String get_prefix() const;
 
 	void apply();
+	void set_custom_arrow_step(const double p_custom_arrow_step);
+	double get_custom_arrow_step() const;
 
 	SpinBox();
 };